Fusible element for protecting electrical circuits



May 3, 1932. WI T, CLARK 1,856,317

FUSIBLE ELEMENT vFOR PROTECTING ELECTRICAL CIRCUITS Filed May 22, 1930 INVENTOR. MAL/AM Z' ZA/9K A TTORNE Y.

Patented May 3, 1932 WILLIAI 'I'. CLARK. 0F IIIWAUXEE, WISCONSIN I'UBIBLE FOB PB ,OTECTIN'G ELECTRICAL GIBOUITB application mea 'nay sa, laao. seran 1ro. 454,537.

The invention relates tovfusible links or other elements adapted to conduct an electrical current, and 1t resides in a novel .construction of fusible link by means of which a current of electricity is conducted from one point to another in a more eicient manner. A link embodying the invention is composed of a plurality of linearly extending conductors, each possessin electrical and physical properties which di er from the like properties possessed by the other, the diering conductors bein bonded or otherwise united or joined toget er into a bi-metallic integral structure by any of the several processes available for such purpose.

In constructing my improved link, a suitably contoured member having a low melting point characteristic' is selected as the basic or primary element of the conductor,

and-.with this is combined one or more secondary conductors in which the characteristics of the basic or primary conductor are so varied as to constitute the secondary conductor as one of high electrical conducting characteristics, and thus ,produce a fusible link having an electric path of highly conductive nature and also a path of least resistance to the passage of the electrical current,

but retaining the low melting point characistie through which the fuse may function in disrupting an electric circuit due to an excess current above that at which the element is rated, to avoid damage.

In a simple form, and as an instance of practical construction, the invention may be embodied in a strip of zinc reduced in width intermediate its'ends as the basic or primary element, to which may be applied an electrodeposit or coating of element. In all of its forms, added mechanical strength is imparted to the link by the shell-like coating of metal of higher tensile strength, and there results a reduction in resistance losses inherent to all electric circuits having low conductive paths.

The electro-deposit or coating of copper insures a copper-to-copper contact with the copper knife blades or other te'minals to which the ends of the fusible link are con- 50 nected in its practical application. The high copper as a secondary i value of conductance of the secondary coating in the novel link, contributes to the maintenance of a 'minimum temperature caused by the flow of any given quantity of electrical current through the fusible link inasmuch as the electric current always follows the path of least resistance. y

In the foregoing,l I have outlined the nature and purpose of my invention, and will now proceed to describe the same specifically. The novelty residing in the invention will be pointed out in the appended claims.

In the accompanying drawings:

Figure 1 is a perspective view of one form of l1nk constructed inaccordance with my invention;

'Fig'. 2 is a sectional view on the line 2 2, F1g. 1, of the link shown in Fig. 1.

Fig. 3 1s a plan view of a sheet of metal having a low melting point characteristic, preferably zlnc, having bands formed by the electro-deposition of copper on the sides thereof for the purposes of the invention as will later be described.

Fig. 4 is a sectional view on the line 4 4, Fig. 1.

Fig. 5 is a perspective view similar to Fig. 1, showing a modified form of the link. i

Fig. 6 is a sectional view on the transverse line 6 6, Fig. 5.

Fig. 7 is a view similar to Figs. l and 5, showing a further modification.

I have illustrated my invention as composed of a strip of metal having a low melting point characteristic and low conductivity,

to which is bonded one or more lnetallic layers having a high melting point characteristic and high conductivity, and my invention contemplates the joining or union of the metals of dllerent electrical and physical properties by any suitable process, as by electro-deposition, welding, soldering, rolling or otherwise, by any means known in the art, to constitute a bi-metallic integral structure of fusible link, in accordance with the purposes of my invention.

Fig. 3 shows a metal sheet, preferably of zinc, on the opposite sides of which are bands 10 of copper, placed thereon it may be by electro-deposition, and separated from each other by exposed or bare 11 of the zinc sheet, i

so as to provide marginal bands and an interlmiexliate band or a plurality of intermediate The sheet thus prepared is passed between the dies of a blankint press, the action of which istepunch out e preferabl in the novel form shown.

The -bllmking die is composed of two punches, one for the purpose of producing the elongated perforation having an outline resembling somewhat a flattened elli When the sheet is fed into the press, the rst operationmakes the perforation referred to, at the leading end of the sheet. The second punch is for the purpose of imparting the desired exterior contour to the link, and com-- pletes the blanking of the latter and its detachment fromthe sheet. The first operation in which only the rforation of a link is eected, is followed y a 'oint operation in which the elongated per oration ofthe next or second linkis effected at'the time that the leading or rst link iscontoured and separated from the sheet. The full lines in Fig.

3 show. the results of the first complete operation, while the dotted lines show what will be the result of the second complete operation. From this, the succession which follows the step-by-step feeding movement of the sheet inte the blanking press will be apparent.

In effecting the electro-deposit of the copbands 10 upon the metal sheet, as shown in Fig. 3, in the production of the link shown in Figs. land 7, suitable dams will be applied to the sheet in such positions as will ser've`to completely cover the lines 11 of the plate which are not to receive the deposited coating, and so form the bare spaces separating the bands.

lThe complete link is shown in Fig. 1, it havends 12 and 13, an intermediate portion 14 composed of two parts separated by the elongated perforation, and contracted or narrowed in the direction of its width to form neck portions 15 and 16 at each longitudinal edge of the link, connecting respectively the said ends and the longitudinally -divided intermediate portion. The ends 12 and 13 and the intermediate portion 14, are coated upon their sides with an electro-deposit of co per, while the necks 15 and 16 are uncoate The co per coated ends of the fusible link provide or a copper-to-copper contact with the terminals of the circuit in which the link is used, and thus a electrical connection is The high electrical conducting characteristic of the copper creates a path of lesser resistance for the flow of the current in traversing v'the link, and this action decreases the resistance losses and tends to the maintenance of a lower tem rature in the restricted current passages o the link. The uncoated necks 15 and 16 of the fusible link,

inks from the sheet,

Lamai# by reason of theirv low.l melting point charac- -teristic, are immediately responsive to a rush of current above that for which they are rated and by reason of their reduced eros-sectional areaswill create a minimum volume of gases, when blown.

Figs. -5 and 6 show a link blanked from an uncoated sheet of zinc, in the manner before described, and then completely coated with an electro-deposit of cop r, except as to the narrowed or contrac and reduced widthwise neck portions 15 and 16, which will be dammed to prevent such deposit.' The comlplete coating forms an enclosing copper she ,which has a greater tensile than the zinc body which it entirely surrounds except for the contracted or reduced neck portions 15 and 16.

Fig. 7 illustrates a further modification of my invention, infa manner which I have found im arts to it some important, adapations w teen used in connection with elecric curren carrying momen overloads whichA are attendant upon inliytrial weiz circuits. In this construction, thel ble link element is blanked from an uncoated sheet of low melting point characteristic, as before described and is then completely and entirely surfaced with an electro-deposit of copper, or metallic layer otherwise applied, having a relatively higher electrical conductivity and a her melting point charactertistic. This ayer forms a shell which completely encloses the basic element. Whenever in use a momenta rush of current i'n excess of that ifor which the link is rated occurs, the temperature at the narrowed or contracted and restricted widthwise portions 15 and 15" of the link, is raised to and above a point which is n to liquefy the basic element at such restricted widthwise portions, the latter become Huid momentaril The enclosing shell of copper, being of a -gher melting point characteristie than that at which the basic element liqueiies, serves'to confine and maintain the form of such element, notwithstandin its molten condition. In the restoration o? the circuit to its normal operating condition, the temperature in the link decreases, and the molten metal at the restricted portions quickly solidifies, and again assumes its normal state, unimpaired, and in condition for further service. If the excess of current be maintained for a period of longer duration than that attending a momentary overload, the fusible link will flow at the reduced por: tions and function in a normal manner te -`open the circuit.

sides, except at the narrowed portion, a coating of copper to provide high electrical conductivity and afford a copper-to-copper contact with the terminals of the circuit in which the link is disposed.

2. A fusible link comprising a at strip of low melting point characteristic, the said strip being provided with a perforation contracted at points and then widened to form. narrowed portions in the link, the said link having upon its sides, except at the narrowed portions, a coating of copper to provide high electrical conductivity and afford a copperto-copper contact with the terminals of an electric circuit.

3. A fusible link comprising a ilat strip of low melting point characteristic, the said strip being provided with an elongated perforation contracted at points intermediate its length and then widened to form narrowed portions in the link, the said link having upon its sides, except at the narrowed portions, a

coating of copper to provide high electrical conductivity and afford a copper-to-eopper contact with the terminals of an electric circuit.

In testimony whereof, I have signed my name at Milwaukee, this 17th day of May,

WM. T. CLARK. 

